In recent years, a high integration of semiconductor devices and a reduction in a size thereof are promoted, whereby a rapid increase in a capacity thereof and a reduction in a cost thereof are materialized. A package of devices which is represented by a surface acoustic wave (SAW) filter and in which electrode patterns and fine structures are formed on a surface of a single-crystal wafer to exert specific electrical functions is changed in characteristics by covering a surface of functional part thereof with a resin and the like, and therefore it requires a hollow structure so that other objects are not brought into contact with particularly functionally important parts on a surface of the devices. Also, image sensors represented by CMOS and CCD sensors are provided with a hollow structure in which a light receiving section is covered with a glass cover so that the devices are protected from moisture and dusts preventing taking an image and are not cut off from light coming from the outside. In addition thereto, a hollow structure is used as well for protecting movable parts in MEMS (micro electro mechanical system) of high frequency application such as gyro sensors, millimeter radars and the like.
In the above devices requiring a hollow structure, hollow structures have so far been formed by processing and connecting inorganic materials (refer to the following patent document 1). However, the problems that the costs are elevated due to an increase in the number of the components and the number of the processes and that it is difficult to reduce a size thereof and decrease a height thereof due to limitation in terms of a structure thereof have been involved in processing the above inorganic materials (refer to the following patent documents 2 and 3).
A method for forming a hollow structure by a resin film of a non-photosensitive type as an alternate material for the inorganic materials (ceramics) is proposed in order to solve the above problems (refer to the following patent document 4). However, the problems that a reliability in the moisture and heat resistance and the hollow part holding property is uncertain and that drilling an electrode part by a laser beam is necessary for a reduction in a size have been involved as well in the above method, and it is not satisfactory in terms of the quality and the cost.
Accordingly, methods for forming a hollow structure by using photosensitive resins are reported because of the reasons that drilling processing can readily be carried out by photolithography and that the moisture and heat resistance and the hollow part holding property are provided (refer to the following patent documents 5, 6, 7, 8 and 9).    Patent document 1: Japanese Patent Application Laid-Open No. 1996/191181    Patent document 2: Japanese Patent Application Laid-Open No. 2001/244785    Patent document 3: Japanese Patent Application Laid-Open No. 1996/204482    Patent document 4: Japanese Patent Application Laid-Open No. 1994/164292    Patent document 5: Japanese Patent Application Laid-Open No. 2008/227748    Patent document 6: Japanese Patent Application Laid-Open No. 2004/64732    Patent document 7: Japanese Patent Application Laid-Open No. 2008/963    Patent document 8: Japanese Patent Application Laid-Open No. 2008/964    Patent document 9: Japanese Patent Application Laid-Open No. 2008/250200